The present invention relates to a movement controlling device for use, for example, as a variable power optical system used in a copying machine designed to make a magnifying power variable by moving a fixed focus lens, and more particularly to an improved mechanism for driving mirrors placed in between a lens and a projection image plane, for example a circumferential surface of a photoconductive drum, to move synchronously with the movement of the lens.
In a so-called electronic copying machine designed to take copies by an electrophotographic duplicating process, an original mounted on an original tray is illuminated with light emitted from a light source, such as a fluorescent lamp, and an image thus exposed to the light from the light source is formed on an electrophotographic photoconductive drum via an image forming system comprising a lens and mirrors.
A recently developed variable power optical systems is such that the magnifying power of a projected image is varied by varying the distance between the original plane and the lens, and the distance between the lens and the projection image plane (i.e., the surface of the photoconductive drum) by moving the lens as part of the image-forming system in the direction of the optical axis. The aforementioned optical system has a so-called variable power function for taking copies of the original, ranging from original size copies to enlarged or reduced size copies.
In such a conventional variable power optical system employing a fixed focus lens (having a fixed focal length), as shown in FIG. 1, there is provided a mirror unit "C", wherein two mirrors are disposed opposite to each other at right angles between a lens "A" and a photoconductive drum "B". The mirror unit "C" is used to invert an optical path and simultaneously move correspondingly to variations of the distance between the original plane and the lens "A" resulting from the movement of the lens A (direction "X" in FIG. 1) so that an optical image corresponding to an image on the original is formed on the circumferential surface of the photoconductive drum "B".
The lens "A" and the mirror unit "C" are disposed as shown in FIG. 2 and moved.
More specifically, a lens holding member 1A holds lens 1 and is slidable fitted into a guide member 11 provided on a chassis of a machine, whereas a mirror holding member 2 for holding mirrors is slidably fitted into a guide member 13 provided thereon likewise. In the lend holding member 1A, an endless wire 6 is wound on pulleys 12, 12 as well as on pulley 3 which is driven by a motor (not shown) and the lens holding member 1A is driven to move by the endless wire as the motor rotates.
The mirror holding member 2 has to be moved in a predetermined relationship with the movement of the lens 1. The mirror holding member 2 is moved by causing a cam follower 25 provided on the mirror holding member 2 to follow a cam 4 which is driven to synchronously rotate with the rotation of pulley 3 for driving the lens that holds member 1A holding the lens 1.
Although almost no problem occurs as long as the magnifying power of the projected image is within a narrow range of 1.4-0.6 times, the movement of the mirrors naturally tends to become greater when the variable range of the magnifying power is widened up to 2.05-0.48 times. With the aforementioned conventional arrangement, the displacement of the cam thus increased allows the cam follower not to follow the cam; the problem is that the mirrors will become unmovable.
In order to solve the above problems, there has been proposed an arrangement wherein the lens and the mirrors are driven by different motors respectively synchronously with each other. However, an increase in production cost becomes unavoidable in this case.